Quell Zen:stones

a bit confused....I have completed the game, found all of the gems but it say's I have not found all of the Zen stones (6 or 7 still missing)....is there any indication in the game where they may be?....the only clue I've seen is a grey circle around the level completion instead of gold on some levels....are these stones only accessable if all levels are completed without buying copletion directions?